Various interchangeable memory cards are often used for the storage and transfer of data in various electronic devices. Such cards are available in several types including, for example, a SIM (Subscriber Identity Module) card to be used in mobile communication devices, as well as a Multimedia Card (MMC), a SD (Secure Digital) card, Memory Stick, and Smart Media, which are registered trademarks. Typically, a memory card is connected to the device by means of conductive contacts.
In most uses, one must make sure that the device and/or the memory card are in a suitable state before they are switched off and/or on. A commonly used method to make sure that the card and the devices are de-energized in the switching situations is to place the memory card in such a way that the power source of the device must be disconnected before the switching, for example by placing the memory card behind a battery. However, since it is not always necessary or advantageous to disconnect the whole device for the time of connecting of the memory card, various solutions have been developed to inform the device about possible connecting of the memory card before the actual connecting operation.
U.S. Pat. No. 6,461,193 discloses an arrangement in which a connector housing for receiving a SIM card comprises a switch which is used to generate a signal when the cover of the housing is closed, and the coupling is opened when the housing is opened, for example for replacing the memory card. This arrangement can be used for forming various information, such as advance warning information.
U.S. Pat. No. 5,718,609 discloses an arrangement in which a metal connector housing for a SIM card is used as a kind of a switch. In the arrangement according to one embodiment of the cited invention, the switches of the housing are coupled to the ground plane when a memory card has been placed in the housing. In a corresponding manner, the coupling is turned off when the housing is opened, for example for replacing the memory card.
A problem in the above-presented arrangements is that various types of electrical interference may be coupled to the advance warning circuit.